The present invention relates to a multilayer circuit board and more particularly to a multilayer circuit board which is suitable for engineering change such as wiring changes.
Wiring changes between semiconductor devices have been conducted by providing engineering change pads (hereinafter referred to as EC pads) to the part mounting plane of a multilayer ceramic substrate, wiring semiconductor devices through said PC pads with possibility for disconnection of intermediate sections of said EC pads, executing wiring changes through disconnection of said intermediate sections and connecting a discrete wire to the EC pads. This system is described in the U.S. Pat. No. 4,245,273.
Moreover, such wiring changes have also been realized by disconnecting between the bonding pads and through holes for wiring nets and connecting a discrete wire to the bonding pads under the condition that connections are guided to a second principal plane from the first principal plane for mounting electronic parts through the through holes. The connections are made through the through holes for connection of internal wiring patterns to the bonding pads for connecting discrete wires. This system is described in the U.S. Pat. No. 4,016,463.
However, in comparison with the former and the latter systems, the discrete wire is laid on the electronic parts mounting plane in the former case while it is laid on the opposed plane in the latter case. But, both systems only allow wiring changes.